1. Field of the Invention
The present invention relates generally to gas transfer devices and more particularly to a percutaneous intravenous oxygenator utilizing hollow gas permeable fibers.
2. Description of the Prior Art
Many types of blood oxygenators are well-known in the art. For example, during open heart surgery, the patient is interconnected with an external oxygenator, commonly known as a heart-lung machine, which introduces oxygen into the blood system. Most types of oxygenators use a gas permeable liquid impermeable membrane. Blood flows along one side of the membrane, and oxygen is supplied to the other side of the membrane. Given a sufficient pressure gradient between the oxygen supply and the blood, the oxygen will diffuse through the membrane and into the blood. In addition, carbon dioxide will tend to diffuse from the blood through the membrane. In other situations, a smaller, implantable oxygenator may be sufficient to adequately supplement the patient's cardiopulmonary function by marginally increasing the oxygen content of the patient's blood. For example, patients suffering from emphysema, pneumonia, congested heart failure, or other chronic lung disease often have blood oxygen partial pressures of approximately 40 torr. A relatively small increase of 10% to 20% is generally sufficient to adequately maintain the patient. This is a particularly desirable alternative in that it avoids the need to intubate the patient in such cases. In addition, temporary use of this type of oxygenator is sufficient in many cases to tie the patient over in acute respiratory insult. Placing such patients on a conventional respirator is often the beginning of a progressive down hill spiral by damaging the patient's pulmonary tree and thereby causing greater dependence on the respirator.
The effective rate of diffusion in percutaneous oxygenators can be limited in some instances by the problem of "streaming" or "channeling," in which the blood stream establishes relatively stable patterns of flow around and through the oxygenator. Portions of the oxygenator are exposed to a relatively high velocity, turbulent flow of blood. These conditions tend to increase cross-diffusion of oxygen and carbon dioxide. However, other portions of the oxygenator are exposed to a low velocity, laminar flow of blood which reduces diffusion of gases. Those portions of the oxygenator immediately adjacent to the regions of the high blood flow may continue to experience high rates of diffusion, but the remaining portions of the oxygenator tend to have relatively low diffusion rates. Thus, the overall diffusion rate of the oxygenator can be substantially diminished by streaming. A number of devices and processes have been invented in the past relating to different types of oxygenators.
U.S. Pat. No. 3,505,686 to Bodell demonstrates the general concept of using gas permeable fibers to boost the oxygen level of blood. The patent discloses several variations of the device wherein it is intended for use inside the body of the patient. In the implantable embodiment of the Bodell device, a tubular casing serves as a shunt either from the pulmonary artery to the left atrium of the heart or more generally between an artery and a vein. A multitude of parallel-connected capillary tubes are used to oxygenate and/or purify the blood circulating to the casing.
U.S. Pat. No. 4,583,969 to Mortenson shows a transvenous oxygenator made of a plurality of small diameter gas permeable tubes connected to headers at each end. However, the specific device disclosed by Mortenson has a significant disadvantage in that two incisions are required.
U.S. Pat. to Taheri No. 4,631,053 discloses a transvenous oxygenator having a single membrane through which oxygen diffuses. The membrane is disposed within a sheath and both are supported by a flexible wire.
U.S. Pat. No. 4,850,958 to Berry, et al. discloses an in vivo extrapulmonary blood gas exchange device having a bundle of elongated gas permeable tubes bound at each end and enclosed within respective air tight proximal and distal chambers. A dual lumen tube is situated relative to the gas permeable tubes such that an outer lumen terminates within the proximal chamber and inner lumen terminates within the distal chamber.
U.S. Pat. No. 4,911,689 to Hattler and U.S. Pat. No. 4,986,809 to Hattler, et al. disclose several embodiments of percutaneous oxygenators. In the simplest embodiment, oxygen is circulated through a plurality of hollow, gas permeable fibers forming loops and the device is inserted through a single incision into a blood vessel. In other embodiments, the fiber loops are bisected and placed in fluid communication within a mixing chamber within a tip at the distal end of the device.
Due to the inherent desirability and need for devices of the above-described type, continuing efforts are being made to improve the efficiency of the gas transferred provided by the device and it is to meet these needs that the present invention has been developed.